1. Field of the Invention
This invention relates to an electrode structure for a silicon semiconductor, a silicon semiconductor device using the electrode structure that can be directly bonded to and mounted on a circuit board without use of bonding wire to enable securement of a large gap (bonding height) between itself and the circuit board at the time of mounting, a method of fabricating the semiconductor device, a circuit board having the semiconductor device mounted thereon, and a method of fabricating the circuit board.
2. Description of the prior art
In recent years, electronic technologies have been increasingly incorporated into virtually every type of device, machine and the like used in the factory, office and home. This in turn has led to an extensive range of electronic components being used for this purpose. The introduction of electronics into such diverse fields has particularly involved the use of very large numbers of circuit boards mounted with electronic control semiconductor devices. As a result, such circuit boards are expanding sharply in range of application, type and number.
Although many kinds of practical circuit boards have been developed and put into use, among circuit boards directly mounted with various semiconductor devices (ICs) bumps and the like, an especially large percentage are adopted for reducing electronic equipment size.
When different types of semiconductor devices etc. are mounted on a circuit board, it is necessary and preferable to leave a gap between the circuit board and the semiconductor device, usually of around 50-100 .mu.m, for injection of sealing resin or to serve as a heat buffer.
Numerous ways have been proposed for providing this gap, which is called the "bonding height" in this specification.
These include, for example, the method of establishing the bond between the circuit portion on the printed-circuit board and the device electrodes by use of a conductive bonding agent, the method of bonding the circuit portion on the printed-circuit board and the chips by fusing solder bumps formed by plating on the chip side, the method of the plating the electrodes of the printed-circuit board and the device electrodes with copper to the required height, further plating them with gold, and bonding them with eutectic solder, the bonding method by gold ball bumps (stud bumps), the bonding method by conductive polymer bumps, the gold-plated resin ball bonding method, the method of bonding by anisotropic conductive film made of microcapsules having insulating resin balls as cores, and the method of bonding by anisotropic conductive film of the metal-ball-core microcapsule type.
Other methods are also available, such as the gold ball bump direct bonding method, but are still too high in cost to be practically applicable.
These conventional methods for establishing bonding height involve a number of shortcomings. When a conductive resin or other such conductive material with relatively high electrical resistance is adopted, the resistance of the bonds is large. On the other hand, when bonding by use of a solder-plated board is adopted, the general practice is to subject the semiconductor device side electrodes to activation processing beforehand. However, this processing is complex and leads to problems of poor spread-out of solder wetting and uneven bonding height. It also results in low reliability of the device connections.
A need has therefore been felt for a way of forming solder bumps on a silicon semiconductor device that enables the silicon semiconductor device to be bonded to a wiring board with high reliability, small bonding resistance, and freely selectable bonding height.
An object of this invention is therefore to provide an electrode structure for a silicon semiconductor device formed with solder bumps of a prescribed height.
Another object of the invention is to provide a solder-bearing silicon semiconductor device that can be directly bonded to a wiring board without use of bonding wire and is highly reliable and small in bonding resistance, and to provide a method of fabricating the silicon semiconductor device.
Another object of the invention is to provide a solder-bearing silicon semiconductor device enabling free selection of the height of solder bumps and to provide a method of fabricating the silicon semiconductor device.
Another object of the invention is to provide a circuit board readily formable with solder bumps at the bond portions (electrode portions) and enabling mounting of a semiconductor device at a freely selectable bonding height between itself and the semiconductor device and to provide a method of fabricating the circuit board.